Butterflies and Moths

Skyrail Nature Diary: February 2015


This month we will be looking at butterflies and moths. These beautiful insects are amongst the most easily spotted and best appreciated of all insects. A common question is what is the difference between butterflies and moths? Well, the main difference is that butterflies are active during the day while moths are active during the night. There are some notable exceptions, like the Four O’clock Moth and the Zodiac Moth - the fact that they the hold the wings open to the side is a typical moth trait. Butterflies always fold their wings over their backs while resting. Another reasonably easy difference to spot is the antennae. Butterflies have slim antennae with clubs on the end while moths have feathery antennae. Butterflies and moths belong to a group of insects characterised by a complex life cycle involving four stages. They start life as an egg and hatch as a larva known as a caterpillar. The caterpillar’s function in the life cycle is to eat, grow and avoid getting eaten. Like all insects, caterpillars grow by moulting (shedding) their exoskeletons at regular intervals, a process known as ecdysis. Once the caterpillar reaches a critical size it finds a safe hiding place and turns into a pupa, known as a chrysalis in butterflies. Moths weave a special cocoon outside the chrysalis, presumably to hide the scent of the living tissue within. Finally the chrysalis splits open and the adult stage, known as an imago, emerges and pumps up its strongly folded wings before letting them dry. The imago is short lived and is only concerned with mating and laying eggs in safe places under the leaves of their principal food plants. Adult butterflies and moths have specialised mouthparts shaped like a curled up double straw designed to feed on the nectar of flowers to fuel their flight. Butterflies and moths can see ultraviolet, which means that what to us looks like white flowers actually have species specific markings on them.

Common Eggfly Butterfly can be found living everywhere in the Wet Tropics and elsewhere in the South Pacific. The males have egg shaped markings with iridescent blue edges on their dark wings. The females have orange patches next to the eggs. These butterflies are very territorial and will attack anything that gets too close. Their principal food plant is the Paste Flower. A few years ago a special disease involving the bacterium Wolbachia that singled out male eggfly butterflies struck in Western Samoa on the islands of Upolu and Savai’i and by 2001, males only made up 1% of the local population. Thankfully the remaining survivors developed resistance to the disease and by 2007 the males made up 40% of the population. 

Cairns Birdwing butterfly is the second largest butterfly in the world, the largest being the related Victoria Birdwing from New Guinea. The males have metallic green wings and a slim blackish body. The females are significantly large with large brownish wings covered in white spots and the thick body is red and yellow. The caterpillars grow up to 12 centimetres and are covered in large black spines. Cairns Birdwing’s principal food plant is the Native Dutchman’s Pipe Vine, a plant that is being partly replaced by an introduced relative toxic to the caterpillars.

Ulysses butterflies are probably the best known of all the butterflies in the Wet Tropics and are used as one of the symbols for the region, together with the cassowary and the fan palm. Both sexes have iridescent blue wings with black edges. The female is a little larger than the male and has small blue crescents on the black edging of the hind wings. Ulysses Butterflies fly higher in the rainforest canopy than any other butterfly and are therefore the most spotted butterfly at Skyrail. Their flight is more akin to that of bird than of butterflies and this fact takes many people by surprise. This butterfly’s principal food plants are Pink Evodia and Kerosene Wood.

Yellow Migrant is one of the few butterflies that actually migrates. Being short lived, each direction of its north to south migration is done over several generations. Exactly how these butterflies navigate is only starting to emerge. Three factors seem important. First there seems to be an instinctive ability to recognise passing landscapes. Secondly, butterflies seem able to navigate by using the position of the stars, perhaps by sensing polarized light emitted by the stars. And finally butterflies seem to orient themselves in relation to the earth’s magnetic field. The males have yellow undersides on their wings while only the hind wings are yellow on the top. The top of the front wings are white with black borders. Females have duller wings with a curved row of spots on the front wings. The caterpillars grow up to 4 centimetres and are green with a thin white stripe running the length of the body with series of three black dots just above it. This butterfly’s principal food plants are Kolomana and Glossy Shower.